This invention relates to accelerator beam optics and, more particularly, to shaping charged particle beams for confining the beam energy to a circular distribution over a selected target area.
For radiation therapy, waste transmutation, tritium production, etc., it is necessary to generate a charged particle beam having a uniform spatial distribution. There are several methods used to make a uniform irradiation. Some of these methods scan a small beam spot over the extent of the target. Other methods spread the beam by multiple scattering in an absorber material and, by tailoring the absorber shape and thickness, smooth the non-uniform beam distribution.
More recently, a system of multipole magnets has been used to spread a small, non-uniform (e.g., Gaussian or triangular distribution) beam and transform it to a nearly spatially uniform rectangular distribution. U.S. Pat. Nos. 4,736,106 and 4,962,317 teach the use of octupole magnets to spread a charged particle beam in two dimensions to produce a beam having a highly uniform particle distribution over most of a rectangular target located at a predetermined distance from a beam source. There are, however, many instances where circular targets are required, and the use of a rectangular beam would result in the loss of substantial beam energy outside of the target area.
Accordingly, the object of the present invention is to provide a circular charged particle beam with a substantially uniform spatial particle distribution at a predetermined target location.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.